Control system for surfacing apparatus



P 1954 c. G. BEATTIE ETAL 3,149,439

CONTROL SYSTEM FOR SORFACING APPARATUS Filed July 16, 1963 4 Sheets-Shet 1 Fig.I.

INVENTORS. CLIFFORD G. BEATTIE 8 WMBERT their AT TORNEY CONTROL SYSTEM FOR SURFACING APPARATUS Filed July 16, 1963 4 Sheets-Sheet 2 INVENTORS. CLIFFORD G. BEATTIE 8 VICTO 0. GUMBERT 74/377 their ATTORNEY Sept. 22, 1964 c. G. BEATTIE ETAL 3,149,439

CONTROL SYSTEM FOR SURFACING APPARATUS Filed July 16, 1963 4 Sheets-Sheet I5 I I I I 2I2 IL I I I I32 -H I I -I- am I l IIT3L I42 I26 I28 j I I I REL [H2 224 I I I I IT I V I I I72 I I L 2z2/."I I I I 6 10 I I I I 2 I I I 68 MOTOR I I4 I I ,I; I I I 7) G Mcoumcu; 244k ,4 22s I I 31'. RESERVOIR 7g (5 I I 236 X 235/ 237 I I A L L74 I 4 ens I 23B 240 r "L' I 2|8 22a I I6 I r18! 474 I Fi 3 I82 9 INVENTORS CLIFFORD G.BEATT|E 8 W TOR .GUMBERT e I I 44 50 7 their ATTORNEY United States Patent 3,149,439 corvraor. svsrnra non sonracnvc APrAnArns Clifiord G. Beattie, Natrona Heights, and Victor D. Ginnhert, Spiingdaie, ia, assignors to Allegheny Lurlium Steei Corporation, Breckenridge, Pa, a corporation of iennsylvania Filed July 16, 1963, 591. No. 295,425 14 Claims. (Cl. 5134) This invention relates to a system for controlling equipment adapted to work upon or condition the surface of a workpiece, and more particularly to a system of the type described for controlling equipment adapted to remove the entire surface layer of a workpiece.

This application is a continuation-in-part of copending application Serial No. 191,997, filed May 2, 1962, now abandoned, and assi ned to the assignee of the present application.

Although not limited thereto, the present invention is particularly usable with a grinder of the type adapted to remove the surface layer of stainless steel slabs or the like. The necessity for grinding becomes apparent when it is remembered that during hot rolling of the steel from the ingot to a semi-finished form, a scale is formed on the slab together with a variety of ingot defects and some defects arising during heating or rolling. If the scale and defects are not removed, they will be carried through to the finished form, resulting in an inferior product.

In the usual slab grinder, the slab to be ground is placed upon a stationary table, while the grinding wheel is motor driven and mounted on the forward end of a boom which is pivotally mounted on a carriage reciprocable on tracks extending adjacent the table and parallel to the long transverse dimension of the slab to be ground. In most cases, the boom extends perpendicular to the tracks and is mounted on guideways to permit it to reciprocate in a direction which is transverse to the direction of movement of the carriage (i.e., parallel to the short transverse dimension of the slab). The boom is reciprocated by fluidoperated cylinder and piston means, While the pressure on the grinding wheel is controlled by second cylinder and piston means having one end pivotally connected to the carriage and another end pivotally connected to the boom structure. The carriage is usually driven by hydraulic motor means operatively connected to the Wheels which ride on the aforesaid tracks, although this may be varied to suit requirements.

In the grinding operation, the entire surface of the slab is usually removed. In the past, this has been accomplished by an operator who sits on the aforesaid carriage and, by means of control levers mounted on an operators console, manually manipulates the carriage back and forth along its tracks and the boom back and forth across the short transverse dimension of the slab until the entire surface of that slab is ground. Although the manual control of a slab grinder of this type is satisfactory, it requires the constant attention of an operator, a task which is tedious and requires large amounts of labor. In a single steel plant, for example, there may be twenty or more such grinders, each requiring a separate operator.

As an overall object, the present invention provides means for automatically controlling surfacing equipment, in general, and a slab grinder of the type described above, in particular, whereby the entire surface of the slab or other workpiece will be ground or otherwise worked upon without the need for manual manipulation of control levers by an operator. Thus, the invention provides a means for relieving the operator of a tedious and timeconsuming task and at the same time provides a means for obtaining a more uniformly ground surface.

In accordance with the invention, the aforesaid grind- 3,149,439 Patented Sept. 22., 1964 we I ing wheel is caused to traverse the surface of the slab back and forth along its long transverse dimension with the grinding wheel being advanced along the short transverse dimension of the slab at the completion of each long transverse stroke of the wheel. In this manner, the entire surface of the slab is ground from one long trans verse edge to the other, the apparatus being coordinated by electrical control means such that the carriage and boom will be automatically guided over the slab or other workpiece to grind the entire surface without the need for manual guidance by an operator.

Specifically, there are provided switch devices adapted to be actuated at the extreme limits of reciprocating movement of the carriage on its tracks, and circuit means including the switch devices for causing first motor means to reverse the direction of movement of the carriage along its tracks whenever an extreme limit of travel is reached while causing second motor means to advance the boom and the grinding wheel or other tool carried thereby in increments along the short transverse dimension whenever at least one of the switch devices is actuated. In this manner, the grinding wheel will be caused to sweep back and forth across the long transverse dimension of the slab and periodically advanced along the short transverse dimension until the entire surface is ground. Preferably, additional switch means are provided for disabling the grinding apparatus when the entire surface has been ground.

In one embodiment of the invention limit switches are used to control the extreme limits of travel of the surfacing tool such that it will reverse its direction of travel Whenever it reaches an edge of the workpiece to produce a back-and-forth action from one edge to the other. An additional limit switch is employed to stop the operation after the entire workpiece has been surfaced. Such limit switches, however, require manual adjustment (i.e., a change in physical location) for each workpiece surfaced since the sizes of the workpieces and their positioning on the workpiece supporting table vary. This is a somewhat cumbersome and time-consuming task on the part of the operator since he must leave the operators console and Walk around the machine to position the limit switches. Therefore, in another embodiment of the invention, and in accordance with another object thereof, means are provided whereby the operator can adjust the limits of travel by means of controls located on the operators control console and without leaving the control cab. As will be seen, such controls include magnetic amplifiers incorporated in bridge circuits such that the physical location of the grinding wheel can be matched by an appropriate adjustment of a potentiometer at the control console.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying rawings which form a part of this specification, and in which:

FIGURE 1 is a top view of a slab grinder of the type with which the present invention may be used;

FIG. 2 is a side view of the slab grinder of FIG. 1;

FIG. 3 comprises a shematic diagram of the hydraulic control system for the slab grinder of FIGS. 1 and 2 together with a schematic diagram of the electrical control system therefor; and

FIG. 4 is a schematic circuit diagram of an alternative control system incorporating magnetic amplifiers.

Referring now to the drawings, and particularly to FIGS. 1 and 2, a slab 10 to be ground is positioned on a stationary support or a table comprising a series of spaced frame members 12. Adjacent the slab 16 and substantially parallel thereto are a pair of tracks 14 and 16 which carry, for reciprocating movement, the slab grinding apparatus generally indicated by the reference numeral 18.

As shown, the grinding apparatus 18 comprises a carriage 19 having, at one end, an operators platform 20 provided with a seat 22 (FIG. 1). Above the platform 20 is a control console 24 having levers 26 thereon for manually controlling the grinding apparatus in a manner hereinafter described. Extending upwardly on one side of the operators platform 20 is a transparent shield 28 which protects the operator from small flying pieces of hot metal produced during the grinding operation. Adjacent the operators platform 20, on the side opposite the shield 28, is a control box 30 which houses the electrical control apparatus for the grinder, hereinafter described.

As best shown in FIG. 2, the carriage 19 is mounted for reciprocating movement on tracks 14 and 16 by means of wheels 32 and 34. These wheels are driven by means of a reversible hydraulic motor, hereinafter described, to cause the carriage to move backwardly and forwardly along the tracks. Mounted on the carriage 19 is a trunnion 36 which carries a boom structure 38 for pivotal movement about an axis, generally indicated at 39 in FIG. 2. Boom structure 38 includes a reciprocable column 40 (FIG. 1) which is surrounded by a bellows arrangement 42 and which carries at its forward end a grinding wheel 44, the grinding wheel being adapted to rotate about an axis which extends generally parallel to the surface of the slab 10. Mounted adjacent the boom structure 38 is a platform 46 adapted to reciprocate on guideways 48 backwardly and forwardly together with the column 49 of the boom structure itself. Hydraulic cylinder and piston means, not shown in FIGS. 1 and 2, is provided for simultaneously reciprocating the column 40, the grinding wheel 44 carried thereby, and the platform 46 backwardly and forwardly, thereby causing the grinding wheel to traverse the slab 10 along a direction extending parallel to its short transverse dimension. Carried on the platform 46 is an electric motor 56 which is connected through a gear reducer 52 to a belt drive 54, this belt drive being adapted to rotate the grinding wheel 44. Carried on the rearward end of the boom structure 38 is a housing 56 which encloses a counterweight, not shown. As is well known to those skilled in the art, the counterweight is provided to maintain constant the downward force on the grinding wheel 44 regardless of how far it extends outwardly over the slab 10. The counterweight is actuated by the aforesaid hydraulic cylinder and piston apparatus which moves the platform 46 and the column 40, and is arranged such that when the grinding Wheel 44 moves outwardly over the slab 10, the counterweight likewise moves 7 outwardly in the opposite direction to produce the desired balancing effect. Also connected to the boom structure 38 is a second hydraulic cylinder and piston apparatus which serves to exert a downward force on the column 40 and the grinding wheel 44, this second hydraulic cylinder and piston apparatus being shown more in detail in .FIG. 3.

inafter described, to cause the piston of cylinder 58 to advance the grinding wheel in increments.

The hydraulic pressurefor cylinders 58, 6t) and 62 is supplied by a first hydraulic pump 64; whereas the hydraulic pressure for a wheel-driving motor 66 for wheels 32, 34 is supplied by a means of a second hydraulic pump 68. Both of the pumps 64 and 68 are driven, as shown, by means of an electric motor 70 which is controlled through motor control circuit 72.

The pump 64, for example, has its input port connected to a reservoir 74 and its output port connected through conduit 76 to an inlet port of a spool valve 78. The

valve 78 has three operative positions, and in the position shown, the conduit 76 will be connected to conduit 80. When, however, the spool valve is shifted to the right as shown in FIG. 3 by a solenoid 82, the conduit '76 will be connected to a conduit 84, thereby pressurizing the cylinder 58 to move its piston to the left. At the same time, the valve will connect the conduit 80 to conduit 85, this latter conduit being connected to the opposite end of the cylinder 58 to permit liquid to be discharged from the forward variable volume chamber of the cylinder. When the spool valve 78 is shifted to the left by solenoid 86, however, the conduit 76 will then be connected to the conduit whereas the conduit 80 will be connected to conduit 84. Thus, the piston of cylinder 58 will now be caused to move to the right. When neither of the solenoids 82 or 86 is energized, the springs 88 and 90 will cause it to assume its central position wherein the conduit 76 is connected directly to conduit 80 while conduits 84 and 85 are blocked.

The conduit 80, in turn, is connected to a second spool valve 92 which, like valve 78, is controlled by two solenoids 94 and 96, the valve being centered by means of springs 98 and 100. With neither of the solenoids 94 nor 96 energized, and the valve centered, the conduit 89 will be connected directly to conduit 102. When, however, the solenoid 94 is energized, the spool valve 92 will sln'ft to the right to connect conduit 86 to conduit 104, this conduit being connected to the lower end of the boom pressure cylinder 60. At the same time, when the spool valve 92 is shifted to the right by solenoid 94, the upper end of the boom cylinder 60 will be connected through conduit 106 to the conduit 162 to permit liquid to be discharged from the upper variable volume chamber of the cylinder. When solenoid 96 is energized, the situation is reversed. That is, the conduit 39 will now be connected through conduit 1136 to the upper end of the boom pressure cylinder 60; whereas the lower end of the same cylinder will be connected through conduit 164 to conduit 162 to permit liquid to be discharged from the lower chamber of the cylinder.

It will be appreciated that the two cylinders 58 and 60 are connected in series, with any fluid entering the cylinders being delivered through conduit 76, and any fluid leaving the cylinders being delivered through conduit 192. Conduit 102, in turn, is connected to a two-position spool valve 108. As shown, the valve 198 is normally urged by a spring 110 to a position wherein the conduit 1132 is connected to conduit 112, this latter conduit being connected to the reservoir 74. Conduit 112, it will be noted, is also connected to the right-hand chamber of the metering cylinder 62. When, however, the solenoid 114 is energized to shift the spool of the valve 168 to the right as viewed in FIG. 3, the conduit 102 will then be connected to the conduit 116, thereby pressurizing the left end of the cylinder 62. The piston of cylinder 62, it will be noted, is normally urged by a spring 118 into the position shown. When, however, the left end of the cylinder is pressurized through conduit 116, the piston will be forced to the right until the end 120 of its piston rod engages the stop 122 which may be adjusted to the right or left by turning the screw 124. Thus, when the left end of the cylinder 62 is pressurized through conduit 116, the piston will move to the right until it strikes the stop 122, at which point the cylinder can move no further and a back pressure will be created in conduits 116 and 162.

Reverting again to the pump 68, it is connected through conduit 126 to a spool valve 128 which is similar in construction to the valves 78 and 92 already described. The spool valve. 128 is normally urged into its central position shown by springs 131) and 132. With the valve in its central position, the conduit 126 will be connected directly to the return conduit 112. That is, the fluid will simply flow through the valve back to the reservoir 74.

When, however, the solenoid 134 is energized, the spool of the valve 128 will shift to the right, thereby connecting conduit 126 to conduit 136 and conduit 112 to conduit 133. This will cause the hydraulic motor 66 to rotate the wheels 32, 34 in one direction. On the other hand, when solenoid 149 is energized, the spool of valve 128 Will shift to the left whereby conduit 125 will be connected to a conduit 138 while conduit 136 is connected to the return line 112. Consequently, under the conditions just described wherein the solenoid 149 is energized, the hydraulic motor 65 will cause the wheels 32, 34 to rotate in the opposite direction.

Connected between conduit 76 and the return conduit 112 is a first relief valve 142 which will open when the pressure in conduit 76 exceeds a predetermined level. Similarly, a second relief valve 144 is connected between the conduit 126 and the return conduit 112, this relief valve 144 being adapted to open when the pressure in the conduit 126 exceeds a predetermined level.

In the operation of the hydraulic control system of FIG. 3, if it is desired to move the column 46 and grinding wheel outwardly (i.e., to the left as shown in FIG. 2), the solenoid 82 will be energized to connect conduit 76 to conduit 84, thereby forcing the column outwardly. If neither of the solenoids 94 nor 96 is energized at this time, fluid will be discharged from the left end of the cylinder 58 through conduit 85, conduit 80, and valve 92 to conduit 162. Furthermore, if the solenoid 114 is not energized, the liquid will simply be discharged through valve 103 to the return conduit 112. If either of the solenoids 94 or 6 is energized, then the action is the same as that described above with the exception that the boom pressure cylinder may move upwardly or downwardly, depending upon which one of the solenoids 94 or 96 is energized and the relative loads on cylinders 58 and 60. That is, the action is the same as that previously described with the exception that the cylinder 6% is now connected in series with cylinder 58, and one or both of the pistons within the cylinders may move depending upon their relative loadings.

If solenoid 114- is energized, the conduit 162 will be connected to conduit 116, thereby forcing the piston in the metering cylinder 62 to the right as viewed in FIG. 3 until its forward end 129 strikes the stop 122. At this point (i.e., when end 120 strikes stop 122), no further fluid can flow into the cylinder 62 through conduits 116 and 192, meaning that if valve 78 is shifted to the right or left, for example, the column 40 will advance only in an amount determined by the movement of the piston within the metering cylinder 62. Actually, when the piston within the metering cylinder stops, a back pressure is created in conduits 115 and 1tl2 and 76. This back pressure will cause the relief valve 142 to open, the relief valve serving to maintain a sufficient pressure within the system to maintain the column 419 at a fixed position. Upon deenergization of the solenoid 114, the spool in valve 168 will move back into the position shown whereby the fluid on both sides of the metering cylinder 62 is discharged to the reservoir 74 such that the spring 113 will return the piston of the metering cylinder back to its original position. It can be seen that in this way the column 40 can be caused to move outwardly over the slab in increments, the length of each increment being determined by the position of the stop 122 associated with the metering cylinder 62.

With reference, now, to the electrical control system for the hydraulic system already described, it includes two terminals 148 and 15'9 for connection to a source of either alternating or direct current voltage. If it is desired to control the grinder manually, the manual switch 152 will be closed, thereby connecting lead 154- to the input terminal 148. In the manual control system are six switches identified as M-1, M2, M-3, M4, M-5 and M-6. With the manual switch 152 closed, closure of switch M-1 energizes solenoid 82, thereby causing the column 46 to be advanced outwardly toward the slab. Similarly, closure of switch M-2 will energize solenoid 86 to cause the column 4i) to be retracted. Closure of switch M-3 will energize the solenoid 96 to cause the piston within the boom pressure cylinder 60 to move in one direction; whereas closure of switch M4 will cause solenoid 94 to become energized to reverse direction of movement of the boom pressure cylinder. Finally, closure of switches M5 and M-6 will energize solenoids and 134, respectively, to cause the hydraulic motor 66 to move the carriage 19 backwardly or forwardly on the tracks 14- and 16 as the case may be.

In the manual operation of a grinder such as that shown in FIGS. 1 and 2, the operator will manually manipulate the switches M-1 to M6 to cause the carriage 19 to move backwardly and forwardly parallel to the long transverse dimension of the slab while at the same time causing the grinding wheel 44 to move inwardly or outwardly parallel to the short transverse dimension of the slab. t can readily be appreciated that in this process the entire surface of the slab may be ground under the manual control of the operator. Usually, the operator will position the grinding wheel over one long transverse edge of the slab 1t? and then cause the carriage 1h to traverse the tracks 14 and 16, the operator periodically advancing the column 413 and the grinding wheel 4-4 carried thereby until the entire surface of the slab is ground.

As was mentioned above, the resent invention is concerned with means for automatically controlling the grinding apparatus whereby it will grind the entire surface area of the slab without the necessity for manual control by the operator. In the particular embodiment of the invention shown herein, two limit switches LS-l and LS2 (FIG. 1) are provided along the track 16. These limit switches are adjustable in position and are arranged such that limit switch LS-l, for example, will be tripped when the grinding wheel reaches one edge of the slab 16 while the limit switch LS-2 is tripped when the grinding wheel reaches the opposite edge. With reference to FIG. 2, it will be noted that two limit switches LS-3 and LS 4 are provided on carriage 19 and are adapted to be engaged by a projection 156 on the carriage 46 which carries motor 59 and reciprocates backwardly and forwardly with the grinding wheel 44. The limit switches LS3 and LS4 are also adjustable in position and are arranged such that limit switch LS4, for example, will be tripped when the grinding wheel reaches the long transverse edge of the slab nearest the carriage 19; whereas the limit switch LS3 will be tripped when the grinding wheel extends out over the other long transverse edge of the slab.

In order to set up the system for automatic operation, the manual switch 152 is first closed and the grinding Wheel manually controlled to move it to the lower left corner of the slab, identified by the reference numeral 18%) in FIG. 1. Thereafter, the limit switches LS1, LS2, LS3 and LS4 are adjusted for the proper dimensions of the slab. That is, the limit switches LS-l and LS?. are spaced apart in an amount equal to the long transverse dimension of the slab 10 with the limit switch LS2 being contacted by the carriage 1 as it will now be at its extreme leftward limit or" travel with the grinding Wheel position over corner 13%. In a somewhat similar manner, the limit switches LS-3 and LS4 will be spaced apart in an amount equal to the short transverse dimension of the slab with the limit switch LS3 contactin the projection 156 on the carriage e6 since the grinding wheel is now in its extreme forward position over the corner 180.

After the grinding apparatus has thus been manually controlled to position the grinding wheel over the corner 180 and the limit switches LS-1 to LS-4 have been placed, the manual switch 152 will be opened while the double pole automatic switch 16%) will be closed. When switch 16% is closed, the input terminal 148 is connected to lead 162 as well as one lead 16 With switch closed and contacts 191 of limit switch LS-3 closed, a circuit is completed through contacts 171 on relay S,

ner thereof as viewed in FIG. 1).

7 which is not now energized, and lead 252 to solenoid 96, thereby actuating valve 92 to pressurize one side of boom pressure cylinder 60 and lift the grinding wheel off of the slab 10.

In order to start the automatic cycle of operation, the start push button 166 is depressed, thereby energizing the relay S. When relay S is energized, normally open contacts 168, 176, 172, 174 and 176 close. Closure of contacts 174 energizes lead 181 which, in turn, actuates the motor control circuit 72 to start motor 7%, thereby causing the hydraulic pumps 64 and 68 to pressurize the conduits 76 and 126. Closure of contacts 176 energizes lead 182 which, in turn, actuates motor control circuit 184 to start the drive motor 5 3 on platform 46 to rotate the grinding wheel 44. Thus, as soon as the start push button 166 is depressed, the pumps 64 and 6% are started as is the motor 51 which rotates the grinding wheel 44. The relay S is held energized after the start push button 166 is released by virtue of the fact that contacts 168 on relay S are now closed, as are the normally closed contacts 186 on relay Av When relay S is energized, it also closes contacts 172 which are adapted to energize relay F. Relay F, however, cannot be energized at this time, since the other side of its coil is connected to lead 173, this lead being adapted to be connected through normally open contacts 175 on relay A to the terminal Since relay A is not now energized, the contacts 175 are open and the lead 173. is :deenergized. Finally, energization of relay S opens its normally closed contacts 171 to deenergize solenoid 96 and return valve 92 to its normal or center position.

After the start push button 166 is released, its contacts 192 close; and since relay S is now energized and its contacts 1715 closed, a circuit is completed through contacts 192, contacts 170, contacts 1% of relay A which is now deenergized, and lead 196 to the solenoid 86, thereby energizing this solenoid to move the spool valve 78 to the left as viewed in PEG. 3. This action connects the pressurized conduit 76 to conduit 85, thereby causing the column 441 and the grinding wheel 44 carried thereby to move toward the tracks 14 and 16 as viewed in FIG. 1 along the left short transverse edge of the slab 10.

The foregoing action (i.e., movement of the grinding wheel inwardly along the leftshort transverse edge) will 7 continue until the limit switch LS4 is contacted, thereby closing its contacts 198. When contacts 1% close, a circuit is completed through contacts 189 on limit switch LS-3, which are now closed, and contacts 1% to energize relay A. Energization of relay A, in turn, opens contacts 194 to deenergize the solenoid 86 on valve 78 whereby the grinding wheel will be positioned substantially at point 2% on the slab 10 (i.e., the upper left-hand cor- When relay A is thus energized, its contacts 175 close to energize lead 173, the relay A being held energized through contacts 1%.

When relay A is energized, it also closes contacts 262, thereby completing a circuit through these contacts, normally closed contacts ZiM- on relay X which is now deenergized, and lead 2% to solenoid 94. This causes the spool of valve 92 to move to the right as viewed in FIG. 3 whereby one side of the boom pressure cylinder 61 will be pressurized to move the grinding wheel, which was previously raised at point 181 (FIG. 1) down into engagementwith the surface of slab 10.

With contacts 175 closed and lead 173 energized, the relay P will be energized through contacts 2513 on limit switch LS2, these contacts being closed at this time since the limit switch LS-Z now contacts the projection 156 on platform 46 (FIG. 2). When relay F is energized, it will be maintained energized by closure of its contacts 210, these contacts being connected through normally closed contacts 212 on relay R, which is now deenergized, to lead 162. Energization of relay F also opens contacts 21 and closes contacts 216. When conviewed in FIG. 2).

tacts 216 are closed, a circuit is completed from lead 162 through the contacts 216 and lead 218 to solenoid 14-8, thereby shifting the spool for valve 128 to the left and causing the hydraulic motor 66 to rotate the wheels 32, 34 such that the carriage 19 will move to the right as viewed in FIG. 1 (i.e., away from limit switch LS2). Thus, as soon as the grinding wheel reaches point 299, it will automatically move along the forward long transverse edge of the slab 1t and along the path of the dotted line until it reaches point 221 At this point, the limit switch LS1 will be engaged, thereby closing its contacts 222 (FIG. 3) to energize relay R which has the other side of its coil connected to the energized lead 173. When relay R is energized, it opens contacts 212, thereby breaking the holding circuit for relay F through contacts 210. After relay R is energized upon closure of contacts 222, it is held energized by closure of its contacts 226, the holding circuit being through contacts 226 and contacts 214 of relay F which are now closed since relay F became deenergized upon opening of contacts 212. When relay R is energized, its contacts 228 are closed to energize lead 23%, this lead being connected to solenoid 134 on valve 128 to shift the spool of the valve to the right and thereby reverse the hydraulic motor 66 and the direction of rotation of wheels 32, 34. Consequently, the carriage 19 will now reverse and move on the tracks 14 and 16 in a direction from limit switch LS1 to limit switch LS-Z.

Before the carriage 19 moves away from switch LS-l, however, energization of relay R closes contacts 232 to energize relay F, this relay being held energized by closure of its normally open contacts 234. With relay P energized, its contacts 236 close, and since contacts 235 on switch LS-1 are now closed with carriage 19 in its extreme right-hand position, the relay X will be energized through contacts 235 and 236 and switch 237. Relay X, in turn, closes its contacts 233 to energize lead 240, this lead being connected to the solenoid 114 to shift the spool of valve 168 to the right as viewed in FIG. 3 against the force of spring 111). The conduit 1tl2 is now connected through conduit 116 to the left end of the metering cylinder 62 to cause its piston to move against the force of spring 113 to the right until end 120 engages the stop 122.

When relay X was energized, it also closed its contacts 2A2 thereby energizing lead 245 which is connected to solenoid 32, thereby shifting the spool of valve 78 to the right as viewed in FIG. 3. This connects the pressurized conduit 76 to conduit 84 to move the column 4% and the grinding wheel 44 outwardly (i.e., right to left as The amount of movement of the grinding wheel, however, is controlled by the amount of fluid which can pass into the cylinder 58. This, in turn, is controlled by the distance which the piston in the metering cylinder 62 can travel. Thus, the incremental travel of the grinding wheel at the completion of each long transverse stroke is controlled by the position of stop 122.

Relays X and R are now energized with the result that the grinding wheel is advanced along the short transverse dimension of the slab by a short increment while the wheels 32, 34 are driven to traverse the carriage 19 to the right, as viewed in FIG. 1. As soon as the carriage leaves switch LS-1, its contacts 235 open to deenergize relay X, however, relay R will remain energized. This will cause the grinding wheel, advanced through one increment, to

travel to the left in FIG. 1 until the limit switch LS2 is contacted, whereupon the relay F will be energized to reverse the direction of movement of carriage 19 on tracks 14 and 16. When limit switch LS-Z is actuated at the completion of the second stroke, it closes its contacts 244 to again energize the relay X and advance the grinding wheel along the short transverse dimension of the slab through an increment determined by the position of stop 122 on cylinder 62. That is, contacts 236 are closed at this time by virtue of the holding circuit for relay P through contacts 234 so that a circuit is again completed to relay X which energ zes to close contacts 242 and energize solenoid 82.

The foregoing action will continue with the carriage traveling back and forth on tracks 14 and 16 and the grinding wheel 44 being advanced in increments at one or both ends of the slab, depending upon whether or not switch 237 is closed. That is, if switch 237 is open, limit switch LS-l cannot energize relay X to thereby energize solenoid 82, and the grinding wheel will be advanced only when limit switch LS-2 is contacted.

If it is desired to stop the grinding wheel at any point during its traverse of the slab, the stop push button 188 will be depressed, thereby opening contacts 24-6. Relay A will now become deenergized to open contacts 175 and deenergize lead 173 together with either relay P or relay R, depending upon which direction the carriage 19 is traveling. At the same time, the depression of stop push button 188 closes contacts 256, and since contacts 171 on relay S are now closed, the lead 252 is energized to energize solenoid 96 and shift the spool valve 92 to the left as viewed in FIG. 3 thereby raising the grinding wheel off of the slab 19. To again start the grinder, the start push button 166 is depressed, thereby closing its contacts 291; and since switch LS-S is not now contacted and its contacts 189 are closed, the relay A will immediately energize and the cycle will progress in the manner described above. At any time during automatic operation, the boom may be moved inwardly or outwardly and/ or the grinding wheel lifted off of the slab by virtue of the fact that lead 154 connected to switches M-1 to M-4 is connected through switch 160, contacts 248 on relay A and contacts 246 on push button switch 188 to the energized lead 162.

When the slab has been completely scanned in the manner described above and reaches the lower long transverse edge as viewed in FIG. 1, the limit switch LS-3 will be contacted, thereby breaking the circuit to relay A and its contacts 250 energizing lead 252 to energize solenoid 96 and raise the grinding wheel 44. At this point, the slab has been completely ground automatically, whereupon the slab may be turned on the table 12 or a new slab placed on the table preparatory to a succeeding cycle of operation.

In summary, the cycle of operation is as follows:

(1) Grinding wheel is moved to point 189 on slab 19.

(2) Switch 152 is opened and switch 169 closed.

(3) Start push button 166 is depressed.

(4) Boom raises grinding wheel off of slab and grinding wheel moves to point 200 on slab.

(5) When point 261) is reached, limit switch LS-4 closes, grinding wheel is lowered onto slab, and carriage 19 moves to the right as viewed in FIG. 1.

(6) At point 22%), griding wheel is advanced one increment (if switch 237 is closed) and carriage moves from right to left as viewed in FIG. 1 along the dotted line.

(7) At opposite end of slab, grinding wheel is again advanced one increment along short transverse dimension of slab and carriage 19 reverses.

(8) Back and forth action continues until switch LS-3 is contacted and the cycle completed with the entire surface of the slab ground.

The embodiment of the invention just described requires, of course, that the operator manually position the limit switches LS-l, LS-Z, LS-3 and LS-4 for each difi'erent slab which is surfaced. This is due to the difference in dimensions of successive slabs and the difference in positioning of the slab on the frame members 12. In the usual case, the operator will manually position the grinding wheel over point 220 shown in FIG. 1 and set the limit switches LS-1 and LS-4. Thereafter, he will manually move the grinding wheel to point 186 and set the limit switches LS-Z and LS-3. At this point the start switch 166 is depressed and the automatic cycle begins. As will be understood, this is a somewhat cumbersome procedure and requires that the operator leave the platform 20 each time the limit switches are set.

A system for eliminating manual positioning of the limit switches by the use of bistable magnetic amplifiers is shown in FIG. 4. The system is essentially the same as that shown in FIG. 3 with the exception that the limit switches LS-1, LS-2 and LS-3 are replaced by relays RS-1, RS-2 and RS-3, respectively. However, the operator no longer needs to position the grinding wheel over points 2211 and 186 and manually adjust the limit switches. Furthermore, this latter system eliminates the need for limit switch LS-4 and its contacts 1%. That is, the limit switch 1.8-4 is replaced by the switch contacts 261 of start switch 166. The contacts 2431, it will be noted, are in parallel with the limit switch LS-4 in FIG. 3 and will serve to initially energize the relay A when the grinding wheel is positioned over point 2% for the reason that contacts 198 on relay RS-3, corresponding to limit switch LS-3, will then be closed.

With the circuit of FIG. 4, the automatic cycle of operation begins at point 2%. Therefore, it is no longer necessary to automatically move the grinding wheel from point 161) to point 201) as shown in FIG. 1, meaning that the circuit of FIG. 3 including contacts 192, and 14 in parallel with the manual switch M-2 are eliminated. Furthermore, since the grinding cycle now starts from point 2110 rather than point 181), the holding circuit for relay S through contacts 168 and 186 can be eliminated since it is no longer necessary to hold relay S energized to close contact 170 while the grinding wheel moves from point 189 to point 201). Aside from these changes, however, the circuit functions in the same manner as previously described with the contacts 261 .of start switch 166 comprising the fourth switch recited in the following claims which is actuated at the inner extreme limit of travel of the grinding wheel defined by the inner edge of the slab 10.

With specific reference to FIG. 4, it will be noted that the relay RS-l which now replaces limit switch LS-l is connected through a diode 2613-1 to the output winding 262-1 of a bistable magnetic amplifier 264-1. As shown, the bistable amplifier 264-1 comprises a core 266-1 of rectangular hysteresis loop material having the output winding 262-1 thereon as well as two input windings 268-1 and 270-1. The input winding 268-1 is connected across leads 162 and 173 corresponding to those shown in FIG. 3. The other input winding 270-1 is connected between the movable tap of a manually adjustable rheostat 272-1 and the movable tap of a potentiometer 34-P.

The rheostat 272-1 is located at the operators control console 24shown in FIGS. 1 and 2 and is provided with a rotatable knob or the like whereby the operator may manually position its movable tap. The potentiometer 34-P, on the other hand, is connected through a mechanical linkage 274 to one of the wheels 34 on which the carriage 19 moves. The mechanical linkage 274 may incorporate gear reducing means such that the tap on potentiometer 34-P will move throughout its range only when the wheel 34 has rotated through a number of revolutions sufiicient to traverse the carriage 19 along its full path of travel on tracks 14 and 16.

It will be readily appreciated that the rheostat 272-1 and the potentiometer 34-P comprise a bridge circuit arrangement which is energized from leads 162 and 173, the output of the bridge circuit appearing across the input winding 2713-1. Normally, the voltage across the input winding 268-1, as determined by the variable resistor 274-1, will be such as'to induce flux in the core 266-1 just beneath its saturation level. Therefore, with no voltage applied across the winding 2711-1, and assuming that an alternating current voltage is applied to input leads 162 and 173, a voltage will be induced across the secondary or output winding 262-1 to energize relay RS-l and thereby reverse the positions of contacts 222, 224 and 235 shown in FIG. 4. When, however, a volt- 1 1 age is applied to winding 279-1, the core 266-1 will abruptly saturate whereby no voltage will be induced in the output winding 262-1 and the relay RS-l will remain deenergized with the contacts 222, 224 and 235 in the positions shown.

No voltage will be induced across the winding 270-1 only when the bridge circuit comprising rheostat 272-1 and potentiometer 34-1 is balanced. By adjusting the rheostat 272-1 such that the bridge circuit will be balanced when the grinding wheel reaches the right edge of the slab as shown in FIG. 1, the relay RS-l will become energized when the right edge of the slab is reached to close contacts 222 and 235 and open contacts 224. in the same manner as limit switch LS-l shown in FIG. 3.

In order to establish the conditions in the bridge circuit whereby the relay RS-l will become deenergized at the right edge of slab 10, the grinding wheel is manually guided, for example, to point 220 shown in FIG. 1.

When the bridge is not balanced and relay RS-l is deenergized due to saturation of the core 266-1, contacts 276-1 on relay RS-1 will be closed to energize an indicating lamp 278-1 located on the operators control console 24 in FIGS. 1 and 2. However, by adjusting the rheostat 272-1 to the point where the bridge circuit is balanced with the grinding wheel at point 220, the voltage across winding 27 -1 will fall to the point where the core 266-1 becomes unsaturated and the relay RS-l is energized, thereby opening the contacts 276-1 to extinguish the lamp 278-1. Consequently, by adjusting the rheostat 272-1 and observing the lamp 278-1 until it is extinguished, the operator can determine the point of balance .of the bridge for the right edge of the slab as shown in FIG. 1. In actual practice, the operator will usually adjust the rheostat in one direction until the lamp 278-1 is extinguished, whereupon he will reverse the direction of movement of the rheostat to the point exactly where the'lamp 273-1 again becomes energized.

The circuit for controlling relay RS-2 corresponding to limit switch LS-2 in FIG. 3 is the same as that for relay RS-1, the potentiometer 34-? also being connected in a bridge circuit arrangement with a second potentiometer 272-2 located at the operators control console 24. In .order to adjust the rheostat 272-2, the operator will manually guide the grinding wheel to point 2%, for example, whereupon he will adjust rheostat 272-2 until the lamp 278-2 is extinguished. Thereafter, he will re- 77 verse the movement of the rheostat to the point just where the lamp 278-2 is again energized. With this arrangement, it can. be seen that as the grinding wheel moves back and forth transversely across the slab, the relay RS-l will become energized when the right edge of the slab is reached as shown in FIG. 1 to close contacts 222 and 235 while opening contacts 244; and relay RS-2 will become energized when the left edge of the slab is reached to close contacts 298 and 224.

The relay RS-3, corresponding to limit switch LS-S in FIG. 3 is controlled by a circuit similar to that for relays RS-l and RS-2. In this case, however, the bridge ometer 58-1 having its movable tap connected through a mechanical linkage 2843 to the boom 40 of cylinder 58, the mechanical linkage 280 being such that as the boom moves outwardly, the movable tap on potentiometer SS-P will be caused to move across its stationary resistance element. Again, relay RS-3 will become energized to close contacts 191 and open contacts 189 only when the bridge circuit comprising elements 272-3 and SS-P is balanced. This, of course, should occur when the grinding wheel reaches the outer edge of the slab furthest removed from carriage 19. Accordingly, the grinding wheel is initially positioned at the outer edge by the operator and the'rheostat 272-3 adjusted until relay RS-3 becomes energized to open contacts 276-3, whereupon the lamp 278-3 is extinguished. Thereafter, the rheostat is adjusted backwardly just to the point where the lamp 12 278-3 is again energized. During the grinding operation, relay RS-S will not become energized in the automatic cycle of operation until the outer edge .of the slab is reached, the operation being the same as that of FIG. 3 where limit switch LS-3 is energized at the completion of the grinding operation.

The operation of the embodiment of the invention just described may be summarized as follows:

(1) After the slab is placed on the frame members 12, the operator manually controls the equipment to move the grinding wheel to the right edge of the slab shown in FIG. 1 and adjusts rheostat 272-1 until lamp 278-1 is extinguished. He thereafter reverses the rheostat until the lamp 278-1 is energized.

(2) The operator manually controls the equipment to move the grinding wheel to the left edge of the slab as shown in FIG. 1 and adjusts the rheostat 272-2, using the indicating lamp 278-2 to obtain the null condition.

(3) Thereafter, the operator manually controls the boom 40 to move the grinding wheel to the edge of the slab furthest removed from carriage 19 and adjusts the rheostat 272-3 using the indicating lamp 278-3 to obtain a null in the manner described above.

(4) Following adjustment of rheostats 272-1, 272-2 and 272-3, the operator manually controls the machine to move the grinding wheel to point 200 shown in FIG. 1. Thereafter, switch 152 is opened and the switch is .closed. Finally, start push button 166 is depressed whereupon the automatic cycle of operation is initiated.

It will be appreciated that in both embodiments of the invention, a switch must be actuated at each edge of the slab in order to control the automatic cycle of operation. In the case of the embodiment of FIG. 3, the four switches comprise the limit switches LS-l, LS-Z, LS-3 and LS-4; whereas in the embodiment shown in FIG. 4 the switches comprise relays RS-l, RS-2 and RS-3 together with the start push button switch 166.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. In workpiece surfacing apparatus having a surfacing tool, suppporting means for supporting a generally rectangular workpiece to be surfaced, first motor means for producing relative reciprocating movement between the tool and the supporting means in a first direction, and second motor means for producing relative movement between the tool and the supporting means in a second direction which is transverse to said first direction; the improvement which comprises first and second switch devices which are actuated at the limits of relative reciproeating movement between the tool and the supporting means in said first direction, a third switch device which is actuated at one limit of relative movement between the tool and the supporting means in said second direction, a fourth switch device which is actuated at the other limit of relative movement between the tool andthe supporting means in said second direction, the limits of relative movement of the tool and the supporting means in said first and second directions being at the edges of said workpiece, circuit means including said first and second switch devices for causing the first motor means to reverse the direction of relative movement along said first direction whenever a limit of travel is reached while causing said second motor means to produce relative movement between the tool and the supporting means in increments along said second direction whenever at least one of the first and second switch devices is actuated, apparatus included in said circuit means for initiating operation of said first motor means when the fourth switch device is actuated, and apparatus included in said 33 circuit means for stopping said first and second motor means when the third switch device is actuated.

2. In workpiece surfacing apparatus having stationary supporting means for supporting a workpiece to be surfaced, a first carriage movable along a path adjacent one long transverse edge of said workpiece, a second carriage on the first carriage and adapted for relative movement with respect to the first carriage along a path which is transverse to the path of travel of the first carriage and along the short transverse dimension of the workpiece, and a surfacing tool on the second carriage adapted to engage a workpiece on said stationary supporting means; the improvement of first motor means for producing reciprocating movement of said first carriage along its path of travel, second motor means for producing reciprocating movement of the second carriage and the tool carried thereby along its transverse path of travel, a first pair of switch devices which are actuated at the extreme limits of reciprocating movement of the first carriage, a second pair of switch devices which are actuated at the extreme limits of reciprocating movement of the second carriage, the extreme limits of reciprocating movement of the first carriage being at the edges of the workpiece along the path of travel of the first carriage and the extreme limits of reciprocating movement of the second carriage being at the edges of the workpiece along the transverse path of travel of the second carriage, circuit means including one of said second pair of switch devices for causing the first motor means to initially advance the first carriage along its path of travel, apparatus in said circuit means including said first pair of switch devices for causing the first motor means to reverse the direction of movement of said first carriage whenever an extreme limit of travel is reached while causing the second motor means to advance said second carriage and the tool carried thereby in increments away from the first carriage whenever at least one of the first pair of switch devices is actuated, and means including the other of said second pair of switch devices for stopping movement of said first and second carriages when an extreme limit of travel of the second carriage is reached.

3. In workpiece surfacing apparatus having stationary supporting means for supporting a workpiece to be surfaced, a first carriage movable along a path adjacent said supporting means, a second carriage on the first carriage and adapted for relative movement with respect to the first carriage along a path which is transverse to the path of travel of the first carriage, and a surfacing tool on the second carriage adapted to engage a workpiece on said stationary supporting means; the improvement of first and second switch devices adapted to be actuated at the extreme limits of reciprocating movement of the first carriage, a third switch device adapted to be actuated at the extreme limit of movement of the second carriage away from the first carriage, a fourth switch device adapted to be actuated at the extreme limit of movement of the second carriage toward the first carriage, means including the third switch device for causing the surfacing apparatus to initiate an automa ic cycle of operation, and means including said first, second, third and fourth switch devices for controlling said automatic cycle of operation.

4. In workpiece surfacing apparatus having stationary supporting means for supporting a workpiece to be surfaced, a first carriage movable along a path adjacent said supporting means, a second carriage on the first carriage and adapted for relative movement with respect to the first carriage along a path which is transverse to the path of travel of the first carriage, and a surfacing tool on the second carriage adapted to engage a workpiece on said stationary supporting means; the improvement of first motor means for producing reciprocating movement of said first carriage along its path of travel, second motor means for producing reciprocating movement of the second carriage and the tool thereby carried along its transverse path of travel, first and second switch devices adapted to be actuated at the extreme limits of reciprocating movement of the first carriage, a third switch device adapted to be actuated at the extreme limit of movement of the second carriage away from the first carriage, a fourth switch device adapted to be actuated at the extreme limit of movement of the second carriage toward the first carriage, circuit means including said third switch device for causing the second motor means to move the second carriage toward the first carriage, circuit means including said first and fourth switch devices for causing said first motor means to move the first carriage along its path of travel from one extreme limit of movement to the other, circuit means including said first and second switch devices for causing the first carriage to reciprocate back and forth along its path of travel between its extreme limits of travel, and circuit means including at least one of said first and second switch devices for actuating the second motor means to advance the second carriage away from the first carriage in an incremental amount whenever said one of the first and second switch devices is actuated.

5. The improvement of claim 4 including means for actuating the second motor means to advance the second carriage in increments when each of said first and second switch devices is actuated.

6. In workpiece surfacing apparatus having a surfacing tool, supporting means for supporting a workpiece to be surfaced, first motor means for producing relative reciprocating movement between the tool and the supporting means in a first direction, second motor means for producing relative movement between the tool and the supporting means in a second direction which is transverse to said first direction, and third motor means for elevating or lowering the surfacing tool with respect to a workpiece on said supporting means; the improvement which comprises first and second switch devices which are actuated at the extreme limits of relative reciprocating movement between the tool and the supporting means in said first direction, third and fourth switch devices which are actuated at the extreme limits of relative movement between the tool and the supporting means in said second direction, said extreme limits of relative movement being at the edges of said workpiece, circuit means including said first and second switch devices for causing the first motor means to reverse the direction of relative movement along said first direction whenever an extreme limit of travel is reached while causing said second motor means to produce relative movement between the tool and the supporting means in increments along said second direction whenever at least one of the first and second switch devices is actuated, circuit means including one of said third and fourth switch devices for causing the third motor means to elevate the surfacing tool off of a workpiece on said supporting means, circuit means including the other of said third and fourth switch devices for causing the third motor means to lower the surfacing tool onto a workpiece carried on said supporting means, and circuit means including said one of the third and fourth switch devices for stopping said first and second motor means after a workpiece has been surfaced.

7. In workpiece surfacing apparatus having stationary supporting means for supporting a workpiece to be surfaced, a first carriage movable along a path adjacent said supporting means, a second carriage on the first carriage and adapted for relative movement with respect to the first carriage along a path which is transverse to the path of travel of the first carriage, and a surfacing tool on the second carriage adapted to engage a workpiece on said stationary supporting means; the improvement of first motor means for producing reciprocating movement of said first carriage along its path of travel, second motor means for producing reciprocating movement of the second carriage and the tool carried thereby along their transverse path of travel, third motor means for elevating or .15 lowering said surfacing tool with respect to a workpiece positioned on said supporting means, first and second switch devices adapted to be actuated at the extreme limits of reciprocatingmovement of the first carriage, a

third switch device adapted to be actuated at the extreme limit of movement of the second carriage away from the first carriage, a fourth switch device adapted to be actuated at the extreme limit of movement of the second car- 'riage toward the first carriage, circuit means including said third switch device for causing the third motor means to elevate the surfacing tool off of the workpiece and for causing the second motor means to move the second carriage toward the first carriage, circuit means including said first and fourth switch devices for causing said third motor means to lower the surfacing tool into contact with 'said workpiece and for causing said first motor means to move the first carriage along its path of travel from one extreme limit of movement to the other, circuit means including said first and second switch devices for causing the first carriage to reciprocate back and forth along its path of travel between its extreme limits of travel, and circuit means including at least one of said first and second switch devices for actuating the second motor means to advance the second carriage away from the first carriage in an incremental amount whenever at least said one of the first and second switch devices is actuated.

8. The improvement of claim 7 and including circuit means responsive to actuation of the third switch device upon movement of the surfacing tool away from the first carriage for causing said third motor means to elevate the surfacing tool off of the workpiece at the completion of a surfacing operation.

9. In workpiece surfacing apparatus having stationary supporting means for supporting a workpiece to be surfaced, a first carriage movable along a path adjacent said supporting means, a second carriage on the first carriage and adapted for relative movement with respect to the first carriage along a path which is transverse to the path of travel of the first carriage, a surfacing tool on the second carriage adapted to engage a workpiece on said stationary supporting means, and motor means for elevating or lowering said surfacing tool with respect to a workpiece carried on said supporting means; the improvement of first and second switch devices which are actuated at the extreme limits of reciprocating movement of the first carriage, a third switch device which is actuated at the extreme limit of movement of the second carriage away from the first carriage, a fourth switch device which is actuated at the extreme limit of movement of the second carriage toward the first carriage, said limits of movement being at the edges of said workpiece, means including said first, second, third and fourth switch devices for controlling an automatic cycle of operation of said surfacing apparatus, means including said third switch device for causing said motor means to elevate the surfacing tool off of said workpiece, and means including said fourth switch device for causing the motor means to lower the surfacing tool onto said workpiece.

10. In workpiece surfacing apparatus having a surfacing tool, supporting means for supporting a workpiece to be surfaced, a first motor means for producing relative reciprocating movement between the tool and the sup- 'porting means in a first direction, and second motor means for producing relative movement between the tool and the supporting means in a second direction which is transverse to said first direction; the improvement which comprises switch devices which are actuated at the extreme limits of relative reciprocating movement between the tool and the supporting means in said first direction, said limits of relative reciprocating movement being at the edges of said workpiece along said first direction, each of said switch devices including a bridge circuit arrangement having first and second potentiometer devices in its opposite legs and arranged to actuate the switch device when the bridge circuit arrangement is balanced, each of 16 said potentiometer devices being provided with a movable tap, one of said taps being manually adjustable and the other being operatively connected to said first motor means such that the tool may be positioned at an edge of the workpiece along said first direction and the manually adjustable top moved to a position where the bridge circuit arrangement is balanced, and circuit means including said switch devices for causing the first motor means to reverse the direction of movement along said first direction whenever an extreme limit of travel is reached while causing said second motor means to produce relative movement between the tool and the supporting means in increments along said second direction whenever at' least one of the switch devices is actuated.

11. In workpiece surfacing apparatus having a surfacing tool, supporting means for supporting a workpiece to be surfaced, a first motor means for producing relative reciprocating movement between the tool and the supporting means in a first direction, and second motor means for producing relative movement between the tool and the supporting means in a second direction which is transverse to said first direction; the improvement which comprises switch devices adapted to be actuated at the limits of relative reciprocating movement between the tool and the supporting means in said first direction, said limits of relative reciprocating movement being at the edges of said workpiece along said first direction, each of said switch devices including a bridge circuit arranged to actuate the switch device when the bridge circuit is balanced, said bridge circuit in each of the switch devices including a potentiometer having a movable tap operatively connected to said first motor means such' that the bridge circuit will be balanced to actuate the switch device when the tool is at an associated one of the edges of said workpiece, and circuit means including said switch devices for causing the first motor means to reverse the direction of movement along said first direction whenever an extreme limit of travel is reached while causing said second motor means to produce relative movement between the tool and the supporting means in increments along said second direction whenever at least one of the switch devices is actuated.

12. In workpiece surfacing apparatus having a surfacing tool, supporting means for supporting a workpiece to be surfaced, first motor means for producing relative reciprocating movement between the tool and the supporting means in a first direction, and second motor means for producing relative movement between the tool and the supporting means in a second direction which is transverse to said first direction; the improvement which comprises first and second switch devices which are actuated at the limits of relative reciprocating movement between the tool and the supporting means in said first direction, said limits of relative reciprocating movement being at the edges of the workpiece along said first direction, each of said first and second switch devices including a bridge circuit arrangement having first and second potentiometer devices each provided with a movable tap and arranged to actuate the switch device when the bridge circuit arrangement is balanced, one of said taps being manually adjustable and the other being operatively connected to said first motor means such that the tool may 'be positioned over an associated one of said edges and a manually adjustable and the other being operatively connected to said second motor means such that the tool may be positioned at the edge of the workpiece along said second direction and the last-mentioned manually adjustable tap positioned to balance the bridge circuit arrangement whereby the third switch device will be actuated at said edge, circuit means including said first and second switch devices for causing the first motor means to reverse the direction of relative movement along said first direction whenever a limit of travel is reached while causing said second motor means to produce relative movement between the tool and the supporting means in increments along said second direction whenever at least one of the first and second switch devices is actuated, and apparatus included in said circuit means for stopping said first and second motor means when the third switch device is actuated.

13. The improvement of claim 12 and including a fourth switch device included in said circuit means for initiating movement of the first and second motor means.

14. In workpiece surfacing apparatus having stationary supporting means for supporting a workpiece to be surfaced, a first carriage movable along a path adjacent said supporting means, a second carriage on the first carriage and adapted for relative movement with respect to the first carriage along a path which is transverse to the path of travel of the first carriage, a surfacing tool on the second carriage adapted to engage a workpiece on said stationary supporting means, and motor means for elevating or lowering said surfacing tool with respect to a workpiece carried on said supporting means; the improvement of first and second switch devices which are actuated at the extreme limits of relative reciprocating movement of the first carniage, a third switch device which is actuated at the extreme limit of movement of the second carriage away from the first carriage, means including said first and second switch devices for controlling an automatic cycle of operation of said surfacing apparatus, and circuit means including said third switch device for causing said motor means to elevate the surfacing tool ofi of said workpiece.

References Cited in the file of this patent UNITED STATES PATENTS 1,866,212 Hurford et a1. July 5, 1932 2,068,529 Baldenhofer Jan. 19, 1937 2,671,294 Cornell Mar. 9, 1954 3,052,067 Dilks Sept. 4, 1962 

1. IN WORKPIECE SURFACING APPARATUS HAVING A SURFACING TOOL, SUPPORTING MEANS FOR SUPPORTING A GENERALLY RECTANGULAR WORKPIECE TO BE SURFACED, FIRST MOTOR MEANS FOR PRODUCING RELATIVE RECIPROCATING MOVEMENT BETWEEN THE TOOL AND THE SUPPORTING MEANS IN A FIRST DIRECTION, AND SECOND MOTOR MEANS FOR PRODUCING RELATIVE MOVEMENT BETWEEN THE TOOL AND THE SUPPORTING MEANS IN A SECOND DIRECTION WHICH IS TRANSVERSE TO SAID FIRST DIRECTION; THE IMPROVEMENT WHICH COMPRISES FIRST AND SECOND SWITCH DEVICES WHICH ARE ACTUATED AT THE LIMITS OF RELATIVE RECIPROCATING MOVEMENT BETWEEN THE TOOL AND THE SUPPORTING MEANS IN SAID FIRST DIRECTION, A THIRD SWITCH DEVICE WHICH IS ACTUATED AT ONE LIMIT OF RELATIVE MOVEMENT BETWEEN THE TOOL AND THE SUPPORTING MEANS IN SAID SECOND DIRECTION, A FORTH SWITCH DEVICE WHICH IS ACTUATED AT THE OTHER LIMIT OF RELATIVE MOVEMENT BETWEEN THE TOOL AND THE SUPPORTING MEANS IN SAID SECOND DIRECTION, THE LIMITS OF RELATIVE MOVEMENT OF THE TOOL AND THE SUPPORTING MEANS IN SAID FIRST AND SECOND DIRECTIONS BEING AT THE EDGES OF SAID WORKPIECE, CIRCUIT MEANS INCLUDING SAID FIRST AND SECOND SWITCH DEVICES FOR CAUSING THE FIRST MOTOR MEANS TO REVERSE THE DIRECTION OF RELATIVE MOVEMENT ALONG SAID FIRST DIRECTION WHENEVER A LIMIT OF TRAVEL IS REACHED WHILE CAUSING SAID SECOND MOTOR MEANS TO PRODUCE RELATIVE MOVEMENT BETWEEN THE TOOL AND THE SUPPORTING MEANS IN INCREMENTS ALONG SAID SECOND DIRECTION WHENEVER AT LEAST ONE OF THE FIRST AND SECOND SWITCH DEVICES IS ACTUATED, APPARATUS INCLUDED IN SAID CIRCUIT MEANS FOR INITATING OPERATION OF SAID FIRST MOTOR MEANS WHEN THE FOURTH SWITCH DEVICE IS ACTUATED, AND APPARATUS INCLUDED IN SAID CIRCUIT MEANS FOR STOPPING SAID FIRST AND SECOND MOTOR MEANS WHEN THE THIRD SWITCH DEVICE IS ACTUATED. 